Spin-wave magnetization of Fe(110)/Ag(111) superlattices: Quasi-two-dimensional versus three-dimensional temperature dependence and anisotropy effects.

Abstract

Recent experimental data, showing a dimensional crossover of the T-dependent magnetization in molecular-beam-epitaxy grown Fe(110)/Ag(111) superlattices with different Ag-spacer thickness, are theoretically reanalyzed, using a simple free-spin-wave theory. We consider a Heisenberg model of localized spins with intraplane and interplane exchange interactions. As suggested by the experimental results, we also take explicitly into account the effect of easy-plane and easy-axis surface anisotropies, which are shown to play an important role in the stabilization of the long-range order, more evident for large thickness of the Ag spacer. The spin-wave dispersion curves and the magnetization are calculated in the framework of a Green's-function method and the correct asymptotic forms for the temperature dependence of the spin deviation in the quasi-two-dimensional regime (T lnT) and in the three-dimensional one (${\mathit{T}}^{3/2}$) are obtained. Further experimental investigation is suggested, in order to point up the anisotropy effects.